All subjects will be required to have their morning assessment conducted between the hours of 7AM and 11AM. Clinical chemistry, serum phosphorus, intact parathyroid hormone(iPTH), plasma fibroblast growth factor 23 (FGF-23),serum 1,25 di-hydroxyvitamin D, serum 25-OH vitamin D, and a spot urine will be collected. A 24-hour urine sample will also be collected.